Genesis of the 1000-Foot Arecibo Dish

The giant radar/radio astronomy dish near Arecibo, Puerto Rico, was conceived by William E. Gordon in early 1958 as a back-scattering radar system to measure the density and temperature of the Earth’s ionosphere up to a few thousand kilometers. Gordon calculated the required size of the antenna by using the Thomson cross-section for scattering by the electrons, and assuming that the elementary scattered waves would be incoherent. During the summer and autumn of 1958 Gordon led a study group that published a design report in December 1958. The report showed that a dish 1000 feet in diameter would be required, and described a limestone sinkhole in Puerto Rico that would make a suitable support for such a dish. Meanwhile, in November 1958, Kenneth L. Bowles per-formed an ionospheric radar experiment that showed that the Gordon calculation for the scattered power was roughly correct, but that the calculated spectral width was too big. The consequence of these results was that a dish substantially smaller than 1000 feet could have satisfied the original goals for the radar. However, from the spring of 1958 the value of 1000 feet had been in the minds of the study team, and a large suite of important experiments that such a dish could do had been identified. These apparently became the raison d’être for the project, and the possibility of shrinking the dish to accomplish only the original goals seems to have been ignored. The project was sold to a new federal funding agency, the Advanced Research Projects Agency (ARPA), which was interested, in part at least, because ballistic missiles traveled through the ionosphere and it was important to fully understand that environment. Gordon’s original calculation contained a remarkably beneficial error. Without it, it is doubtful that such a large dish would have been built

PUBLIC POLICY EDUCATION: A CHALLENGE FOR THE 90'S

Teaching/Communication/Extension/Profession,

Introduction to very-long-baseline interferometry

Long-baseline interferometry achieves high resolution by using two or more widely separated radio telescopes and recording video signals on magnetic tapes, which are later brought together and cross-correlated. This paper contains discussions of the coherence and timing requirements and of calibration procedures. Applications to measuring brightness distributions and to spectroscopy are reviewed briefly. Some pertinent phenomena connected with radio-wave scattering in irregular media are discussed

OJ 287 as a Rotating Helix

We present preliminary data from high-cadence 15-GHz VLBA images of OJ 287 from 1995 to 2015. The ridgelines suggest that the jet is rotating, perhaps with a period of∼30 years. The EVPA of the core rotated by 240° in 2001–2002 and decreased slowly after that. The inner jet apparently moved to a new direction after the rotation,as shown by the emergence of a new component at a new PA at 43 GHz, in 2004. This was presaged by a strong rise in the flux density of the core, and then its sudden fall as the new component was identified. The equivalent sequence of events took place about 5 years later at 15 GHz, but in addition the core EVPA had a step in 2006 and moved to be aligned with the new 43-GHz component. The 15-GHz core became optically thin in 2006, but the angular resolution was insufficient to separate the new component from the core until 2010

A History of OVRO: Part II

Before the advent of big, national radio-telescope arrays, Caltech's Owens Valley Radio Observatory was a worldwide mecca for interferometry

Interview with Marshall H. Cohen

Interview with Marshall H. Cohen, Caltech Professor of Astronomy, emeritus, by Shelley Erwin in six sessions and a supplement, 1996-1997, and 1999. He talks about his youth, family background, and education, and his early interest in electrical gadgets; wartime work for Westinghouse; higher education at Ohio State University: bachelor’s degree, electrical engineering, 1948; PhD in physics, 1952. Reminiscences of the Ohio State Antenna Lab and Vic Rumsey, 1952-1954. Following appointment at Cornell in electrical engineering, Cohen describes his transition to the new field of radio astronomy. Recalls early participants in the field: J. Greenstein, F. Whipple, M. Ryle, B. Lovell, R. Hanbury Brown, E. G. Bowen, J. Bolton, P. Wild, W. Christiansen; British and Australian competition in interferometry; Caltech’s early entry in the field. Brief interlude recalls Richard Feynman both at Cornell and later at Caltech. Recalls establishment of National Radio Astronomy Observatory (NRAO), Green Bank, West Virginia; later sites in New Mexico. Cohen’s involvement with ionospheric physics and building of Arecibo telescope in Puerto Rico. Recalls scientific work and political battles over Arecibo; colleagues E. Salpeter, T. Gold, B. Gordon. Cohen’s move to UC San Diego, 1966, and soon after, recruitment to Caltech, 1968. He recalls the developments of the 1960s: first US interferometer in Owens Valley; competition for buildings very large arrays; the Greenstein decadal committee (1970)

OJ 287 as a Rotating Helix

We present preliminary data from high-cadence 15-GHz VLBA images of OJ 287 from 1995 to 2015. The ridgelines suggest that the jet is rotating, perhaps with a period of∼30 years. The EVPA of the core rotated by 240° in 2001–2002 and decreased slowly after that. The inner jet apparently moved to a new direction after the rotation,as shown by the emergence of a new component at a new PA at 43 GHz, in 2004. This was presaged by a strong rise in the flux density of the core, and then its sudden fall as the new component was identified. The equivalent sequence of events took place about 5 years later at 15 GHz, but in addition the core EVPA had a step in 2006 and moved to be aligned with the new 43-GHz component. The 15-GHz core became optically thin in 2006, but the angular resolution was insufficient to separate the new component from the core until 2010

Work extremum principle: Structure and function of quantum heat engines

We consider a class of quantum heat engines consisting of two subsystems interacting via a unitary transformation and coupled to two separate baths at different temperatures $T_h > T_c$. The purpose of the engine is to extract work due to the temperature difference. Its dynamics is not restricted to the near equilibrium regime. The engine structure is determined by maximizing the extracted work under various constraints. When this maximization is carried out at finite power, the engine dynamics is described by well-defined temperatures and satisfies the local version of the second law. In addition, its efficiency is bounded from below by the Curzon-Ahlborn value $1-\sqrt{T_c/T_h}$ and from above by the Carnot value $1-(T_c/T_h)$. The latter is reached|at finite power|for a macroscopic engine, while the former is achieved in the equilibrium limit $T_h\to T_c$. When the work is maximized at a zero power, even a small (few-level) engine extracts work right at the Carnot efficiency.Comment: 16 pages, 5 figure